Multi-projector display systems have become increasingly popular when large-scale, high resolution displays are required. Overlapping projectors to combine the resolution, brightness and size of several projectors into a single display is a well-known method for achieving these goals. Because each of the projectors will have its own geometric position, brightness, color response, and distortion, it is important that the image output by each projector is transformed into a common space to ensure that the individual images combine into a seamless image on the display surface. In order to achieve this, post-processing alignment step is applied to the video signal at each projector. FIG. 1, which is a diagram of an exemplary multiple projector system that can be aligned by the present method, depicts the situation wherein:Aspect ratio A3xL=(wS1+wS2+wS3)/h Iw=w1+w2+w3=(a−G+G−H+H−f) Ih=h 
As shown in FIG. 1, input video sources Ik 103(1)-103(3) are input into an array of video projectors Pk 104 (three projectors P1-P3 are shown) that illuminate a respective surface 105(1)-105(3) whose resulting images Sk 107(1)-107(3) are distorted by the display surface shape, the configuration of the projectors and other factors. The aspect ratio of each input source is h/w and the total aspect ratio of the input image display is defined by each of the input aspect ratios and their configuration. This input size and aspect ratio is simply the combination of each input signal and how those signals are logically configured into an input array. For example, a computer that contains a graphics subsystem with three outputs may be configured into a in a 3×1 configuration as shown to support a wide computer desktop application. The resulting aspect, then, is the sum of the widths SI1 (a-c in FIG. 1)+SI2+SI3.
The goal of multi-projector alignment is to re-map the input images so that when they reach the projector and illuminate the display, they create a seamless image on the screen surface. However, when the input images are geometrically distorted by the alignment process, the aspect ratio of the input source is not typically retained. The goal of alignment has been viewed as independent of both alignment and preserving input image aspect. A proper post-processing step is required to compute an alignment transform that remaps input pixels from each of the source images I1-Ik to an output image that will be aligned physically on the displays surface when the SI1 . . . k images are combined but also preserves the input aspect ratio of the display system.
This is a significant problem because the change in effective aspect ratio, in particular, for projector displays that are dynamically reconfigured or are constructed in an ad hoc manner can lead to significant changes in the display's effective aspect ratio. In FIG. 1, for example a 1×3 array of projectors yields an aspect ratio that is three times the input width by the height of the input. When the projectors are overlapped to create a 1×3 overlapped array of projected images with horizontal overlap only, pixels are effectively “lost” in the overlap zones and impact the display width significantly, while loss of pixels in the vertical direction may be less. This type of alignment transform does not reserve the input aspect of the image and can result in unwanted distortions.
Take, for example, the case when a three-projector system is being driven by three WUXA input signals whose source resolution is 1920×1200 (w=1920, h=1200). If the input signals are configured to be a three-wide-one-high configuration (e.g., a wide screen desktop computer), the resulting aspect ratio is: 5760/1200 or 4.8. When these outputs are used to drive a multi-projector array that is overlapped and then calibrated, the data is remapped into a virtual window whose effective resolution is somewhat less than that of the input source. This new virtual display has a width and height that is determined both by the geometric transform that aligns the input images as well as other constraints including determination of the viewable area (i.e. specification of a rectangular region to which the input video must be mapped). This pixel loss is related to the degree to which the projectors are overlapped, skew on the screen of the projected image, and other factors.
In the previous 1×3 example, there is no overlap between projected images a-G, G-H, and H-f. If it is now, in a second example, assumed that all the vertical 1200 pixels in each projector are retained projected to the screen surface but 10% of the pixels in the horizontal area between the projected displays are lost due to overlap of the adjacent images, then the result is a new aspect ratio of: (5760*0.9)/1200, or 4.32, as indicated by overlapping displays a-c, b-e, and d-f [compare this new aspect ratio with the previous value of 4.8]. Thus, in effect, the alignment transform induces a geometric distortion in all cases except where the lost pixels in the overlapping region exactly match in both the vertical and horizontal directions. However, this is almost never the case. There has been no previous solution that addresses the above problem with aligned projector displays.